This report is in response to section 750 of the William M. (Mac) Thornberry National Defense Authorization Act (NDAA) for Fiscal Year 2021 (FY) (Public Law 116283), "Study on the Incidence of Cancer Diagnosis and Mortality among Military Aviators and Aviation Support Personnel." The Act mandated a study on the incidence of cancer diagnosis and mortality among military fixed wing aviators (aircrew) and aviation support personnel (ground crew). This report presents the findings from the Phase 1-a study, which observed that military aircrew and ground crew were overall more likely to be diagnosed with cancer, but less likely to die from cancer compared to the U.S. population. A Phase 1-b study has been initiated which includes additional data from the Department of Veterans Affairs Central Cancer Registry (VACCR) as well as data from 46 State cancer registries. The findings from the Phase 1-a study and implications for the Phase 2 study are provided below.